Pigment concentrates are produced by digesting pigments in a liquid carrier medium using shearing machines and thus finally dispersing them in such a way that the pigment is permanently present in the form of the primary particles. Suitable shearing machines are known to the expert and are described, for example, in
C. H. Hare, Protective Coatings--Fundamentals of Chemistry and Composition, Technology Publishing Comp., Pittsburgh (1994) PA1 H. Kittel, Lehrbuch der Lacke und Beschichtungen, Vol. III, pages 239 et seq, Verl. W. A. Colomb, Berlin, Oberschwandorf (1976) PA1 J. V. Robinson, R. N. Thompson, Dispersants, in Paper Coating Additives, Monograph No. 25, TAPPI, Atlanta 1963 PA1 J. D. Schofield, Polymeric Dispersants, in Handbook of Coating Additives, L. J. Calbo (Ed.), Vol. 2, Marcel Dekker, New York Basel, Hong Kong (1992). PA1 C. Baumann, D. Feustel, U. Held, R. Hofer, "Stabilisierungssysteme fur die Herstellung von Polymer-Dispersionen", in: Welt der Farben, pages 15 et seq. (February 1996) PA1 Fette & Ole 26 (1994), pages 47-51 PA1 Speciality Chemicals 1984 (May Number), pages 17, 18, 22-24 PA1 Fat Sci. Technol. 95 (1993) No. 3, pages 91-94 PA1 Otto-Albrecht Neumuller, Rompps Chemie-Lexikon, 7the Edition, Stuttgart 1974, pages 2693-2695. PA1 where R is a linear saturated alkyl chain containing 8 to 22 carbon atoms and (G).sub.p is a glycoside or oligoglycoside unit with a degree of oligomerization x of 1 to 10, for deinking waste paper. Alkyl glycosides corresponding to general formula (IV) are very well-known surface-active agents which can be obtained by acetalization from sugars and aliphatic, primary alcohols containing 8 to 22 carbon atoms. A preferred sugar component (glycoses) is glucose although fructose, mannose, galactose, telose, gulose, allose, altrose, idose, arabinose, xylose, lyxose, libose and mixtures thereof may also be used. By virtue of their ready availability and their favorable performance properties, the acetalization products of glucose with fatty alcohols obtainable, for example, from natural fats and oils by known methods, more particularly with linear, primary, saturated and unsaturated C.sub.8-22 fatty alcohols are preferably used. So far as the glycoside unit (G).sub.p is concerned, both monoglycosides (p=1), where a sugar unit is attached to the fatty alcohol by a glycoside linkage, and oligomeric glycosides with a degree of oligomerization p of 2 to 10 are suitable. Mixtures of mono- and oligoglycosides are generally present. Alkyl glycosides (IV), where R is an alkyl containing 8 to 22 carbon atoms and (G).sub.p is a glycoside or oligoglycoside unit with a degree of oligomerization p of 1 to 10, are particularly suitable. In one most particularly preferred embodiment, R is an alkyl group containing 8 to 14 carbon atoms. The average degree of oligomerization is preferably in the range from 1 to 1.5. PA1 where R.sup.9 is a linear saturated alkyl chain containing 8 to 22 carbon atoms, R.sup.10 is hydrogen or a methyl group and the index q is a number of 1 to 50. Particularly preferred compounds (V) are fatty alcohol ethoxylates, more especially addition products of 2 to 20 moles ethylene oxide per mole fatty alcohol containing 12 to 18 carbon atoms.
which is particularly concerned with American technologies. In view of the importance of dispersion to the lacquer, paint and printing ink industry, both the dispersion process and the low molecular weight and relatively high molecular weight compounds suitable for stabilizing the primary particles are described in detail in the specialist literature, cf. for example:
There is no teaching to be derived from the known prior art on the choice of particular additives which effectively support the formulation of pigment concentrates, particularly where these pigment concentrates are intended to allow the production of low-emission or even emission-free paints and printing inks or when they are intended to be free from ecologically or ecotoxicologically unsafe substances.
One particular difficulty lies in the formulation of water-based pigment concentrates, particularly if no low molecular weight co-solvents, such as ethylene glycol or propylene glycol, are to be added. Thus, although so-called pigment dispersants based on polyphosphates or polyacrylates, as the expert well knows, are eminently suitable for keeping pigments and fillers suspended in emulsion paints in conjunction with the latex particles stabilized by emulsifiers or protective colloids, they are not suitable for the production of pigment concentrates with the requirement profile described above.
Most dispersants, which are perfectly suitable in organic carrier oils differing in polarity, fail when water is selected as the continuous phase for the pigment concentrates. Surfactant-based dispersants with a good wetting effect on pigments, such as alkylphenol polyglycol ethers (cf. for example GB 861 223) have recently entered the ecological debate so far as their biodegradability is concerned both in the detergent industry, where they have already been completely replaced as surfactants in Germany, and in emulsion polymerization processes, i.e. in the production of water-based binders for emulsion paints, cf.:
Another complication affecting the choice of additives for the formulation of pigment concentrates is that the dispersing additive has to be selected so that, largely irrespective of the carrier oil, the viscosity of the continuous phase decreases with increasing shear force, i.e. must be pseudoplastic and definitely not dilatant.
Another factor which has to be taken into account in the formulation of pigment concentrates is that a special balance has to be established between water retention capacity and hygroscopicity so that the drying of the concentrate is significantly retarded. Partly dried pigment concentrates are intended to be readily redispersible. On the other hand, water retention capacity and hygroscopicity should not be so high that the final coating is sensitive to water.
Other performance properties of the final paint, such as stability to freezing/thawing, stability in storage, shear stability, should be as little affected in a negative sense as the properties of the cured film, for example transparency, gloss or resistance to blushing.
Another particular requirement to be satisfied by the pigment concentrates to be provided in accordance with the present invention is that they should be compatible with a broad range of binders, organic and inorganic pigments which, in turn, are mostly dispersed in so-called basic lacquers, and at the same time both with water and with the various solvents used in paints and with the highly alkaline waterglasses used in silicate paints.
On an industrial scale, a large percentage of liquid paints is produced by preparing the polymeric binder in a separate stage and then mixing it with the other constituents to form the final paint. If pigmenting is intended to be carried out at this early stage, the pigment is ground with the binder in a preliminary step carried out either in a high-speed mixer or in a dissolver and is then diluted down to the in-use concentration. DIY paints and paints for the professional decorator both for interior and exterior application are of particular interest in connection with the present invention. The binders for these paints are produced by emulsion polymerization in aqueous phase. In practice, the aqueous phase often contains volatile organic solvents, so-called coalescing agents, which are added either during the polymerization itself or at a later stage and which support film formation by partly dissolving the latex particles and promote levelling. The smell of these coalescing agents, particularly the known and widely used isobutyric acid-2,2,4-trimethyl-3-hydroxypentyl ester (Texanol.RTM.), remains noticeable for several days in freshly painted rooms. However, it is becoming increasingly more unacceptable in modern society. Accordingly, there is an interest in keeping modern paints completely free from such coalescing agents and other volatile solvents and co-solvents and in ensuring that they are not carried over into the paints by the pigment concentrates.
Besides the coloring of paints at the production stage, a significant percentage is only colored immediately before use either to establish special tones or to meet special customer requirements. In these cases, an industrially preformed pigment concentrate is added to and mixed with a white or pastel-colored stock paint. This customer-oriented method of coloring can be carried out both by hand and on a semi-industrial or full industrial scale. In cases such as these, the pigment concentrate is generally mixed in a ratio of 5 to 200 ml per l stock paint. A combination of two or three different pigment pastes is often needed to obtain the required color tone. The pigment concentrates usually contain high pigment concentrations, i.e. the pigment volume concentration (or PVC for short) is normally between 10 and 80%.
Ethylene oxide adducts with special glycols containing a --C.ident.C-- group as structural element are known from DE-A-26 28 145. These compounds are said to be suitable as humectants, dispersants, nonionic antifoam agents and viscosity stabilizers and to develop their effect in aqueous solution in lower concentrations than conventional surfactants. Beyond listing the above-mentioned applications, however, DE-A-26 28 145 does not disclose any other concrete details or embodiments.
EP 565 709 B1 discloses water-based inkjet inks which contain polyol/alkylene oxide condensates as co-solvent. According to page 4, lines 9 to 15 of this document, the polyol contains in particular 3 or more OH groups. The polyols explicitly mentioned include in particular special triols, such as glycerol, trimethylol propane, trimethylol ethane, 1,2,4-butanetriol and 1,2,6-hexanetriol; tetrols, such as pentaerythritols and di(tri-methylol propane), pentols, such as glucose, and hexols such as sorbitol and inositol. However, the use of diols is described as unsatisfactory. In this connection, it has been found that alkylene oxide condensates of diols are generally not compatible with pigment dispersions with the possible exception of neopentyl glycol alkoxylates.
DE 195 11 669 A1 describes the use of dimerdiol alkoxylates as thickeners for water-based surface-active compositions, i.e. laundry detergents, dishwashing detergents and cleaners and also hair care and body care formulations.
WO 96/7689 discloses copolymers with the general formula (A--COO).sub.2 --B, where A has a molecular weight of at least 500 and is the residue of an oil-soluble complex monocarboxylic acid of special structure and B has a molecular weight of at least 500 and is the divalent residue of an alkyl glycol or a polyalkylene glycol. The copolymers according to WO 96/7689 are said to be suitable for dispersing inorganic pigments in organic media.
EP 735 109 A2 describes water-based pigment preparations which contain inter alia 10 to 80% of a pigment and 0.1 to 20% of an alkoxylation product obtained by addition of optionally substituted styrenes onto optionally substituted phenols and reaction with ethylene oxide and/or propylene oxide.
DE 39 20 130 A1 describes the use of partial esters of oligoglycerols with fatty acids as pigment dispersants for water-based lacquer dispersions. The partial esters mentioned may optionally be ethoxylated and/or propoxylated.
The problem addressed by the present invention was to provide effective additives for the production of pigment concentrates and the pigment concentrates obtainable with these additives which would meet the numerous criteria mentioned above in regard to the desirable property profile of such additives or the pigment concentrates themselves.